The present invention relates to magnetic devices and in particular to the use of Heusler alloys in magnetic devices.
Heusler alloys may order in the L21 form, a crystal structure that determines the crystal arrangements of the elements in the Heusler alloy with respect to one another.
The Heusler alloys which are of interest exhibit itinerant ferromagnetic behaviour. This means that the magnetic moments which are ferromagnetically ordered below the Curie temperature are associated with electrons which show extended behaviour and are able to move through the material rather than being localised to particular atomic sites.
Certain Heusler alloys exhibit half-metal behaviour below the Curie temperature, in which, at the Fermi energy, there is a band gap in the density of states for one spin direction of the electrons and no band gap—and hence spin-polarised metallic behaviour—in the density of states for the other spin direction.
Heusler alloys which exhibit spin-polarised metallic behaviour as described in the preceding paragraph have been the subject of interest in relation to their possible use in spintronics applications, for instance in spin-polarised tunnel junctions or in magnetic memory read/write heads. Such uses for Heusler alloys exhibiting spin-polarised metallic behaviour require that the alloys are well below their Curie temperature, and thus efforts have been made to find, and to use, Heusler alloys having Curie temperatures far above room temperature.